A huge market exists for disk drives for mass-market computing devices such as desktop computers and laptop computers, as well as small form factor (SFF) disk drives for use in mobile computing devices (e.g. personal digital assistants (PDAs), cell-phones, digital cameras, etc.). To be competitive, a disk drive should be relatively inexpensive and provide substantial capacity, rapid access to data, and reliable performance.
Disk drives typically employ a moveable head actuator to frequently access large amounts of data stored on a disk. One example of a disk drive is a hard disk drive. A conventional hard disk drive has a head disk assembly (“HDA”) including at least one magnetic disk (“disk”), a spindle motor for rapidly rotating the disk, and a head stack assembly (“HSA”) that includes a head gimbal assembly (HGA) with a moveable transducer head for reading and writing data. The HSA forms part of a servo control system that positions the moveable transducer head over a particular track on the disk to read or write information from and to that track, respectively.
Typically, a conventional hard disk drive includes one or more disks in which each disk has a plurality of concentric tracks. Each surface of each disk conventionally contains a plurality of concentric data tracks angularly divided into a plurality of data sectors. In addition, special servo information may be provided on each disk to determine the position of the moveable transducer head.
The most popular form of servo is called “embedded servo” wherein the servo information is written in a plurality of servo sectors that are angularly spaced from one another and are interspersed between the data sectors around each track of each disk. Each servo sector typically includes a preamble generally having at least a track identification (TKID) field and a sector ID field and a group of servo bursts (e.g. an alternating pattern of magnetic transitions) which the servo control system of the disk drive samples to align the moveable transducer head with or relative to a particular track. Typically, the servo control system moves the transducer head toward a desired track during a “seek” mode using the TKID field as a control input. Once the moveable transducer head is generally over the desired track, the servo control system uses the servo bursts to keep the moveable transducer head over that track in a “track follow” mode. During track follow mode, the moveable transducer head repeatedly reads the sector ID field of each successive servo sector to obtain a binary encoded sector ID number that identifies each sector of the track. In this way, the servo control system continuously knows where the moveable transducer head is relative to the disk. Further, position error signals (PESs) are often utilized as a feedback signal for the servo control system during track following operations. The PES signal may be derived from read servo bursts as the head flies over the servo bursts of the servo sectors of the disk. The PES signal may be utilized by the servo control system to keep the head near the center of the track.
Servo sectors are typically written to a disk to define the plurality of evenly-spaced, concentric tracks. Servo sectors may be written to a disk either by an external servo writer or by the disk drive itself as part of a self servo-writing process.
As disk drive manufacturers have been forced to increase data capacity in disk drives to remain competitive, a greater number of tracks are required to be servo-written to each disk to provide for the increased data storage capacity. To accomplish this, the distance between each of the servo-written tracks has been made increasingly smaller. However, when the servo sectors are servo-written, due to the required smaller distance between tracks, erase bands often occur that erase portions of the servo sector, such as the preamble and servo bursts. This may result in degraded tracking and seeking performance during disk drive operation.
In typical self servo-writing disk drives, fixed preamplifier write settings for a given class of disk drives are utilized for all of the heads of the disk drives in the self servo-writing of servo sectors. These write settings of the preamplifier may include settings related to write current (IW), write current overshoot amplitude (OSA), and overshoot duration (OSD). Due to the large variation in characteristics among the heads of a given head population (e.g., a particular type or brand of head), a number of heads may produce large erase bands when utilizing these fixed preamp values. It is desirable to find solutions to avoid erase band damage to servo sectors and degraded servo performance.